The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-024920 filed on Jan. 31, 2001, the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a process for extruding a tube having different sections in its longitudinal direction, and a die for tube extrusion molding used when the tube is extruded. The tube is used for a vehicle for example, particularly for the body frame of a motorcycle.
2. Description of Background Art
A process for extruding a tube used for a member forming the body of a vehicle such as a motorcycle and having variable sections in its longitudinal direction and a die for extrusion used for extrusion molding, respectively, are disclosed in Japanese published unexamined patent application No. Hei 10-286619 (see FIG. 11). This die for extrusion is provided with a fixed female die having a fixed die hole and a slide die which has a slide die hole in the same shape as the fixed die hole and which can be slid on the lower surface of the fixed female die. Two or three fixed cores are arranged in parallel in the fixed die hole via clearance, and two or three slide cores integrated with the slide die are also arranged in parallel in the slide die hole via clearance. The slide core is laminated on the fixed core and can be slid on the fixed core. A tube-like member is formed (hereinafter merely called a tube) in the shape of a letter E or in the shape of the letter E having one more bar in the center of the inside of which a rib for reinforcement. The tube has a sectional form which changes in the longitudinal direction, and is formed by moving the slide die in a direction perpendicular to the direction of extrusion, extruding the material from a communicating part between the slide core and the fixed core, and between the fixed die hole and the slide die hole by the die for extrusion.
Since the width of the reinforcement rib of the above-mentioned conventional type changes, and extends in a longitudinal direction, the enhancement of the rigidity afforded by the rib may not be enough. One example of this is when a tube having a width that changes in the longitudinal direction is used for a part requiring high rigidity against a load that acts from a direction in which the width of the tube changes, such as when it is used as a main pipe of a motorcycle. In this case, the enhancement of the rigidity by the rib may not be sufficient.
In a situation in which a tube is connected to another member and a large load acts on a connection of the tube, in order to keep the tube as light in weight as possible, it is desirable to not to reinforce the whole tube, but only to reinforce the tube in the vicinity of the connection of the tube. However, in the conventional type tube described above, the rib for reinforcement is formed over the entire longitudinal direction of the tube. As such, the rib is formed in a part not requiring the enhancement of the rigidity, increasing the weight of a product using the tube, for example a vehicle. In addition, the amount of the material used for the tube becomes more than the required amount, and the cost of the material is increased. As a result, there is a problem in that the cost of the product using the tube is increased.
Ways to add rigidity selectively to only the part of the tube requiring rigidity have been considered. For example, a reinforcing member could be added by welding to only that part of the tube requiring the rigidity. However, this approach is problematic, in that an increase of manufacturing man hours and the increase of the cost by welding are caused.
Also, it is desirable that rigidity be enhanced only at the end of main pipe that connects to the head pipe. By maintaining a lesser rigidity at the other end of the pipe, ride quality is enhanced due to the spring action of the end of the pipe having less rigidity. However, there is no known conventional die or extrusion method capable of producing a pipe with these requirements.
The present invention is made in view of the above situation. The common object of the present invention is to provide an extrusion molding process wherein a tube having an intermediate wall extended in a direction crossing a direction in which the width of the tube changes can be easily and cost effectively formed. Further, the object of the invention is to provide an extrusion molding process wherein a tube the rigidity of only a required part of which is enhanced by an intermediate wall can be easily formed. An additional object of the invention is to provide a die for tube extrusion molding suitable for embodying the invention.
One aspect of the invention is a process for extruding a tube having different sections wherein a tube is formed by extruding the material via an opening formed by the superposition in the direction of extrusion of a first die hole formed in the first die, and a second die hole formed in the second die. The process uses a die for tube extrusion molding provided with the first die and the second die which are superposed in the direction of extrusion, and which can be relatively moved in a set direction along the superposed surface. The sectional form of the tube is varied in the direction of extrusion by relatively moving the first die and the second die in the set direction. Further, the process is characterized by extruding a tube having different sections through an outflow passage having an opening for a tube wall and an opening for at least one intermediate wall which continues to the opening for the tube wall inside the opening for the tube wall. The opening for the tube wall has a predetermined width extending in a first direction, which is a direction when the set direction is projected on a plane perpendicular to the direction of extrusion, and extends in a second direction crossing the first direction on the perpendicular plane and by relatively moving the first die and the second die in the set direction. Material is then extruded from the outflow passage, forming the wall of the tube, the width in the first direction varying in the longitudinal direction by means of the opening for the tube wall, and simultaneously forming the intermediate wall in the inside space of the tube by means of the opening for the intermediate wall, the intermediate wall having a fixed thickness of the predetermined width in the first direction, and extending in the longitudinal direction and continuing to the tube wall.
Additionally, according to the invention, one or more intermediate walls extended in the second direction crossing the first direction can be easily formed by the opening for the intermediate wall in the inside space of the tube in which the width of the wall formed by the opening for the tube wall varies in the first direction by relatively moving the first and second dies in the set direction. Material is then extruded from the outflow passage, causing the rigidity of the tube to be further enhanced by having one or more intermediate walls formed in the direction crossing the direction in which the width of the tube varies. Cost can also be reduced. In addition, since the intermediate wall can have a fixed thickness corresponding to the predetermined width in the longitudinal direction in situations when the width of the tube varies, the weight of the tube by forming the intermediate wall can be kept to a minimum.
The invention further includes the process for extruding the tube having different sections, whereby the intermediate wall is a connecting wall connecting two tube wall parts opposite in the second direction of the tube wall. This process partitions the inside space into a plurality of independent partial spaces on the section of the tube and a number of the connecting walls in the longitudinal direction of the tube. These spaces are changed by opening or blocking at least one of the openings for the intermediate walls according to the amount of the relative movement in the set direction of the first and second dies.
In addition, the present invention includes a process for producing a tube having high rigidity by forming the connecting wall connecting two tube wall parts opposite in the second direction crossing the first direction in which the width of the tube wall is changed. A tube can be formed with a part having one or more connecting walls and another part having no connecting wall, respectively, in the longitudinal direction. This is accomplished by controlling the amount of the relative movement of the first and second dies. As a result, the tube having a part with connecting walls of different numbers according to the magnitude of required rigidity, can be readily and cost effectively formed. In addition, as the connecting wall is formed in only a part of the tube requiring the high rigidity of the tube, the increase of the weight of the tube can be kept to a minimum, as compared with a tube having a connecting wall is formed over the entire longitudinal length of the tube.
Additionally, the present invention is based upon a die for tube extrusion molding provided with a first die and a second die which are superposed in a direction of extrusion and which can be relatively moved in a set direction along the superposed surface. The first die has a first die hole formed by a void between the first peripheral wall of a first hole formed in the first die and a first core arranged in the first hole and integrated with the first die. The second die has a second die hole formed by a void between the second peripheral wall of a second hole formed in the second die and a second core arranged in the second hole and integrated with the second die. Further an opening formed by the superposition in the direction of extrusion of the first die hole and the second die hole forms the outflow passage of the material of the formed tube. The first core is composed of a plurality of child cores arranged in parallel, having predetermined width in a first direction which is a direction when the set direction is projected on a plane perpendicular to the direction of extrusion and forming a void between at least one of the first cores extended in a second direction crossing the first direction on the perpendicular plane. The outflow passage has an opening for a tube wall formed by a void between the first peripheral wall or the second peripheral wall and the first core or the second core and an opening for a first intermediate wall defined by the void between the first cores and continuing to the opening for the tube wall. The first die and the second die are superposed so that the maximum interval in the first direction of the opening for the tube wall can be varied according to the amount of the relative movement in the set direction of the first die and the second die. The second core keeps at least one of the openings for the first intermediate wall in an open state by the predetermined width and in a blocked state.
The width in the first direction of the wall of the tube can be changed by the outflow passage having the opening for the tube wall formed by the first and second die holes of the first and second dies superposed so that they can be relatively moved in the set direction, and the openings for one or more first intermediate walls opened or blocked by the second core. Thus, the tube can be formed having high rigidity, the result of it having one or more intermediate walls extended in the second direction in the inside space of the tube via the opening for the first intermediate wall, and extended with fixed thickness corresponding to the predetermined width of a void between the first cores in the longitudinal direction. Further, the tube composed of the combination of a part having one or more intermediate walls in the longitudinal direction, and another part having no intermediate wall, can be easily formed by controlling the amount of the relative movement of the first and second dies.
The invention is further characterized in that the void between the first cores is continuously extended in a second direction, the second core is composed of a plurality of child cores arranged in parallel respectively having predetermined width in the first direction, thus forming a void between at least one second cores continuously extended in the second direction. The outflow passage has an opening for a second intermediate wall defined by a void between the second cores and continuing to the opening for the tube wall. The first die and the second die are superposed, so that the first core keeps at least one of the openings for the second intermediate wall in an open state by the predetermined width and in a blocked state, according to the amount of the relative movement in the set direction of the first die and the second die.
The outflow passage has the openings for one or more first intermediate walls opened or blocked by the second core, and continuously extends in the second direction and continuing to the opening for the tube wall. The openings for one or more second intermediate walls are opened or blocked by the first core, and continuously extend in the second direction and continuing to the opening for the tube wall. With the die of the present invention, it is possible to form a tube having high rigidity as a result of the connecting walls, which are two or more intermediate walls extended in the second direction in the inside space of the tube, and extended in the longitudinal direction with fixed thickness corresponding to the predetermined width of a void between the second cores, connecting the tube wall in the second direction. Further, with the present invention, a tube can be easily formed composed of the combination of a part having two or more connecting walls in the longitudinal direction, and another part having one connecting wall, and a third part having no connecting wall. This is accomplished by controlling the amount of the relative movement of the first and second dies according to the magnitude of the rigidity required at every part in the longitudinal direction of the tube.
In this specification, xe2x80x9csuperpositionxe2x80x9d means xe2x80x9cbeing superposedxe2x80x9d. The xe2x80x9csection of the tubexe2x80x9d means the xe2x80x9ccross section of a plane perpendicular to the direction of extrusion or the longitudinal direction of the tubexe2x80x9d.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.